The present invention relates to a new and improved construction of a false twist device of the type embodying a number of friction disks which are coaxially arranged in sequence and thread guide elements helically distributed along the circumference of the false twist device, the thread guide elements extending into the space between the friction disks. Further, this invention pertains to a novel method of producing a textured yarn or the like.
The friction between the thread and the friction surface which is required for imparting twist to the thread is generated, on the one hand, by the coefficient of friction between the thread and the friction surface and, on the other hand, indirectly by the thread tension prevailing at the region of the false twist device. The thread tension directly generates the normal force required for the friction between the thread and the friction surface. Hence, there is generated a friction force between the thread and the friction surface of the false twist device owing to the twist- and thread travel speeds directed at right angles to one another, and which friction force is opposite the direction of travel of the thread and thus produces an additional thread tension.
On the other hand, there prevails the requirement that the maximum applicable thread tension should not become too great so that the individual filaments are not ruptured.
Now in order to at least partially compensate the aforementioned additional thread tension there is disclosed in German patent application 1,660,639 and Czechoslovakian patent 106,286 a false twist device embodying a number of coaxial successively arranged friction disks and thread guide elements extending into the space between the friction disks such that the thread guided by the thread guide elements contacts the disks at a uniform inclination with respect to the circumferential direction. Due to the inclination of the thread guided at the false twist device the friction force transmitted to the thread is resolved into a component imparting twist to the thread and a component which transfers or feeds the thread. This thread transfer component reduces the thread tension required following the false twist device.
The drawbacks of the aforementioned state-of-the-art devices are considered to be the following:
A. Due to the aforementioned resolution of the friction force with inclined arrangement of the thread at the friction disk the imparting of twist is reduced in relation to the circumferential speed of the twisting or friction disks, so that such must be brought to a higher rotational speed corresponding to the reduction in the imparted twist. This requires a correspondingly increased power consumption and furthermore increases the wear of the friction surface.
b. It is known that the last friction disks, and in particular the very last friction disk, viewed in the direction of travel of the thread or the like, imparts by far the greatest proportion of twist to the thread so that such experience an appreciably greater amount of wear, resulting in rapid changes in the friction properties and thus, in turn, in changes in the texturizing characteristics.
c. Moreover, the thread transfer component only can be changed at the expense of the twist imparting component, or vice versa, in such a manner that there can be hardly attained optimum conditions as concerns imparting the twist and the thread tension.